Of conventional hop varieties, there are at least twenty named commercially grown hop varieties in the United States today, and some seventy-five to eighty varieties that are grown around the world. The varieties differ as to assorted physical features such as vine color and structure, as well as cone number, location, size and shape.
Commercial varieties of hop are female hops that exist as a perennial rootstock that produces an annual flush of above-ground, or aerial, vegetation. The perennial rootstock is comprised of a woody crown with a number of main roots and sub-roots that are used for water uptake, nutrient uptake, and winter starch storage. Over the winter, the woody crown supports many buds that develop into main vines (shoots) in the spring, emerge from the ground, and extend to produce the annual above-ground vegetation. In nature, with the onset of frosts in the fall, the above-ground portion of the plant "dies-back" to ground level, and only the perennial rootstock survives into the following year.
A main vine consists of a single flexible cylinder that produces pairs of leaves at nodes separated by variable distances along the length of the vine. The length of main vine between a pair of nodes is known as an internode. A bud is produced in the junction between leaf and vine, which junction is also known by the botanical term axil. Such a botanical term, as well as other botanical terms herein, are generally known to those of skill in the art, and can also be found in standard botanical texts such as Simon, E.W., et al., Lawson's Textbook of Botany--Revised, University Tutorial Press Ltd., London, England, 14th Ed. 1966. The bud grows and develops into a lateral, also known as a side-shoot or side-arm, with the same basic vegetative structure as the main vine. The buds on the laterals develop into groups of flowers that later mature into cones (strobiles). Because the laterals produce and support the cones of the hop, the structure of the laterals strongly influences the number of cones produced and hence the ultimate commercial yield of a variety.
The cones are the useful brewing commodity, and are referred to as "hops" in the commercial industry. Each cone is a group of flowers (inflorescence) consisting of sepals and petals (bracts and bracteoles) mounted on a central strig (or rachis). The resultant structure resembles a small pine cone or fir cone but is non-woody and green in color. In nature, the bracteoles support the seed of the plant.
Complete descriptions of the botanical structure of the hop plant are given in Burgess, "Hops--Botany, Cultivation and Utilization," Weed Crop Series, Interscience Publishers, Inc., New York, 1964 and Neve, "Hops," von Nostrand Reinhold, New York, 1991.
A trellis of poles and wire, commonly 18 feet in height and known as a "high trellis," supports strings that the main vines climb. The main vines grow to the top of the trellis, where they produce the laterals that support the groups of flowers that develop into the cones. Typically, the laterals bear cones only in the upper parts of the plant (i.e., closer to the main vine); the distance from the main vine varies from one variety to another. Under an alternative growing system, the "HopUnion Low Trellis Hop Growing System," the vines are grown on a trellis of single rows of 10 feet in height, like wine grapes (the 10 foot trellis is referred to herein as a "low trellis"). (Lewis, "The HopUnion U.S.A., Inc.--Low Trellis Hop Production System," Proc. Tech. Comm. of the IHGC of the XXXVIIIth International Hop Congress, Hereford, U.K. Published Rijksstation voor Landbouwtechniek, Merelbeke/Gent, Belgium, 17-37, 1990.) Under either system, when the cones are physiologically mature (ripe), the cones are harvested, then dried and compressed into bales for market, where the cones are typically used for the productuion of beverages such as beers, ales and related alcohol-containing liquids.
Different varieties of hops have differences in the chemical constituents of the lupulin of their cones. Accordingly, chemical analysis of such differences can be useful in distinguishing one hop variety from another. Such analysis is generally performed by high pressure liquid chromatography ("HPLC") of the soft resins along with gas liquid chromatography ("GLC") of the essential oils. Recently, Kenny developed a key for differentiation of hop varieties based on chemical analysis of the soft resins. (Kenny, "Identification of U.S. Grown Hop Cultivars by Hop Acid and Essential Oil Analyses," J. Amer. Soc. Brewing Chemists 48(1):3-8, 1990.) Further, Peacock and McCarty, as well as Kenny, have developed keys for the differentiation of hop varieties based on chemical analysis of the essential oils. (Peacock and McCarty, "Varietal Identification of Hops and Hop Pellets," Master Brewer Assoc. of the Americas Technical Quarterly 27:81-85, 1992; Kenny, supra.) These keys are based on gross differences in the amounts of, and ratios between, major constituents, which differences are large enough to overcome variation inherent in the analytical analysis of biological material.